// bbldc_basicdaycount.h                                              -*-C++-*-
#ifndef INCLUDED_BBLDC_BASICDAYCOUNT
#define INCLUDED_BBLDC_BASICDAYCOUNT

#include <bsls_ident.h>
BSLS_IDENT("$Id: $")

//@PURPOSE: Provide a protocol for basic day-count calculations.
//
//@CLASSES:
//  bbldc::BasicDayCount: protocol for basic day-count calculations
//
//@SEE_ALSO: bbldc_basicbasicdaycountadapter
//
//@DESCRIPTION: This component provides a protocol, `bbldc::BasicDayCount`, for
// implementing an arbitrary day-count convention.  Concrete implementations of
// this protocol may implement, say, the ISMA 30/360 day-count convention, or a
// custom day-count convention appropriate for some niche market.
//
// Several of the components in `bbldc` provide individual day-count convention
// support through interfaces that are functionally identical to the abstract
// interface provided by this component, except that they do not inherit from
// `bbldc::BasicDayCount`.  In conjunction with the adapter components (e.g.,
// `bbldc_basicbasicdaycountadapter`), `bbldc::BasicDayCount` is intended to
// allow run-time binding of these and other similar day-count implementations.
//
///Usage
///-----
// This section illustrates intended use of this component.
//
///Example 1: Definition and Use of a Concrete Day-Count Convention
/// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
// This example shows the definition and use of a simple concrete day-count
// convention.  This functionality suffices to demonstrate the requisite steps
// for having a working day-count convention:
// * Define a concrete day-count type derived from `bbldc::BasicDayCount`.
// * Implement the pure virtual `daysDiff` and `yearsDiff` methods.
// * Instantiate and use an object of the concrete type.
//
// First, define the (derived) `my_DayCountConvention` class and implement its
// constructor inline (for convenience, directly within the derived-class
// definition):
// ```
// // my_daycountconvention.h
//
// class my_DayCountConvention : public bbldc::BasicDayCount {
//   public:
//     my_DayCountConvention() { }
//     virtual ~my_DayCountConvention();
//
//     /// Return the (signed) number of days between the specified ...
//     virtual int daysDiff(const bdlt::Date& beginDate,
//                          const bdlt::Date& endDate) const;
//
//     /// Return the (signed fractional) number of years between the ...
//     virtual double yearsDiff(const bdlt::Date& beginDate,
//                              const bdlt::Date& endDate) const;
// };
// ```
// Then, implement the destructor.  Note, however, that we always implement a
// virtual destructor (non-inline) in the .cpp file (to indicate the *unique*
// location of the class's virtual table):
// ```
// // my_daycountconvention.cpp
//
// // ...
//
// my_DayCountConvention::~my_DayCountConvention() { }
// ```
// Next, we implement the (virtual) `daysDiff` and `yearsDiff` methods, which
// incorporate the "policy" of what it means for this day-count convention to
// calculate day count and year fraction:
// ```
// int my_DayCountConvention::daysDiff(const bdlt::Date& beginDate,
//                                     const bdlt::Date& endDate) const
// {
//     return endDate - beginDate;
// }
//
// double my_DayCountConvention::yearsDiff(const bdlt::Date& beginDate,
//                                         const bdlt::Date& endDate) const
// {
//     return static_cast<double>((endDate - beginDate) / 365.0);
// }
// ```
// Then, create two `bdlt::Date` variables, `d1` and `d2`, to use with the
// `my_DayCountConvention` object and its day-count convention methods:
// ```
// const bdlt::Date d1(2003, 10, 19);
// const bdlt::Date d2(2003, 12, 31);
// ```
// Next, we obtain a `bbldc::BasicDayCount` reference from an instantiated
// `my_DayCountConvention`:
// ```
// my_DayCountConvention       myDcc;
// const bbldc::BasicDayCount& dcc = myDcc;
// ```
// Now, we compute the day count between the two dates:
// ```
// const int daysDiff = dcc.daysDiff(d1, d2);
// assert(73 == daysDiff);
// ```
// Finally, we compute the year fraction between the two dates:
// ```
// const double yearsDiff = dcc.yearsDiff(d1, d2);
// // Need fuzzy comparison since 'yearsDiff' is a 'double'.
// assert(0.1999 < yearsDiff && 0.2001 > yearsDiff);
// ```

#include <bblscm_version.h>

#include <bdlt_date.h>

namespace BloombergLP {
namespace bbldc {

                           // ===================
                           // class BasicDayCount
                           // ===================

/// This `class` provides a protocol for determining values based on dates
/// according to derived implementations of specific day-count conventions.
class BasicDayCount {

  public:
    // CREATORS

    /// Destroy this object.
    virtual ~BasicDayCount();

    // ACCESSORS

    /// Return the (signed) number of days between the specified `beginDate`
    /// and `endDate`.  If `beginDate <= endDate`, then the result is
    /// non-negative.  Note that reversing the order of `beginDate` and
    /// `endDate` negates the result.
    virtual int daysDiff(const bdlt::Date& beginDate,
                         const bdlt::Date& endDate) const = 0;

    /// Return the (signed fractional) number of years between the specified
    /// `beginDate` and `endDate`.  If `beginDate <= endDate`, then the
    /// result is non-negative.  Note that reversing the order of
    /// `beginDate` and `endDate` negates the result; specifically,
    /// `|yearsDiff(b, e) + yearsDiff(e, b)| <= 1.0e-15` for all dates `b`
    /// and `e`.
    virtual double yearsDiff(const bdlt::Date& beginDate,
                             const bdlt::Date& endDate) const = 0;
};

}  // close package namespace
}  // close enterprise namespace

#endif

// ----------------------------------------------------------------------------
// Copyright 2015 Bloomberg Finance L.P.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// ----------------------------- END-OF-FILE ----------------------------------
